I. Field of the Invention
The invention relates to subsea well risers, particularly to improved tubing string connections, and more particularly to adjustable metal to metal tubing string joints.
II. Description of the Prior Art
In the oil well industry, certain assemblies have been used for drilling and then producing oil wells in subsea locations. Generally, such assemblies include a riser for carrying a string of drill pipe or for flowing well production fluids upwardly.
The riser is made up of a plurality of riser conduit sections with mating flanges at each end for bolting connection to adjacent conduit sections. Normally provided with the riser conduit sections are various strings of tubing which run parallel and externally of the riser from the well platform down to the wellhead. These tubing strings serve a multitude of functions, including delivering fluids to be used in pumping the well fluids back up the riser, and providing hydraulic fluids to downhole controls. Each riser may have associated with it as many as twelve or more tubing strings.
These tubing strings are also provided in sections which are adapted to be disposed within orifices in their associated riser conduit mating flanges and to be connected to the axially-adjacent tubing string section in the adjacent riser conduit section. It can therefore be appreciated that when the riser conduit mating flanges are mated it is extremely important that the associated tubing string sections be circumferentially aligned and axially aligned so as to allow the tubing string sections to be properly connected and sealed.
In the past, one means of connection between axially-adjacent tubing string sections has been provided as shown in FIG. 3 which illustrates the male end, a, of an upper tubing string section, b, being in a stab-fit sealing engagement with the female end, c, of the lower adjacent tubing string section, d. Because the seal is a stab-fit engagement, the male and female members are free to move axially relative to each other. Such axial movement inevitably occurs during production operations and can produce an unsatisfactory seal. Furthermore, because of the frequent movement of the male and female members, a metal-to-metal seal cannot be used because it would quickly become worn and ineffective; and therefore, non-metal O-rings or other type non-metal seals are used.
The present invention overcomes and avoids the problems attendant to stab-engagement seals by providing a metal-to-metal seal with no axial positioning problems.